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//------------------------------------------------------------------------------
// LG_check_mis: test if iset is a maximal independent set
//------------------------------------------------------------------------------
// LAGraph, (c) 2019-2022 by The LAGraph Contributors, All Rights Reserved.
// SPDX-License-Identifier: BSD-2-Clause
//
// For additional details (including references to third party source code and
// other files) see the LICENSE file or contact permission@sei.cmu.edu. See
// Contributors.txt for a full list of contributors. Created, in part, with
// funding and support from the U.S. Government (see Acknowledgments.txt file).
// DM22-0790
// Contributed by Timothy A. Davis, Texas A&M University
//------------------------------------------------------------------------------
#define LG_FREE_WORK \
{ \
GrB_free (&C) ; \
LAGraph_Free ((void **) &I, NULL) ; \
LAGraph_Free ((void **) &X, NULL) ; \
}
#define LG_FREE_ALL \
{ \
LG_FREE_WORK ; \
}
#include "LG_internal.h"
#include "LG_test.h"
int LG_check_mis // check if iset is a valid MIS of A
(
GrB_Matrix A,
GrB_Vector iset,
GrB_Vector ignore_node, // if NULL, no nodes are ignored. otherwise,
// ignore_node(i)=true if node i is to be ignored, and
// not added to the independent set.
char *msg
)
{
//--------------------------------------------------------------------------
// check and report the results
//--------------------------------------------------------------------------
LG_CLEAR_MSG ;
GrB_Matrix C = NULL ;
GrB_Index *I = NULL ;
bool *X = NULL ;
GrB_Index n ;
GRB_TRY (GrB_Matrix_nrows (&n, A)) ;
int64_t isize ;
GRB_TRY (GrB_Vector_reduce_INT64 (&isize, NULL, GrB_PLUS_MONOID_INT64,
iset, NULL)) ;
GrB_Index nvals ;
GRB_TRY (GrB_Vector_nvals (&nvals, iset)) ;
LAGRAPH_TRY (LAGraph_Malloc ((void **) &I, nvals, sizeof (GrB_Index), msg));
LAGRAPH_TRY (LAGraph_Malloc ((void **) &X, nvals, sizeof (bool), msg)) ;
GRB_TRY (GrB_Vector_extractTuples_BOOL (I, X, &nvals, iset)) ;
// I [0..isize-1] is the independent set
isize = 0 ;
for (int64_t k = 0 ; k < nvals ; k++)
{
if (X [k])
{
I [isize++] = I [k] ;
}
}
LAGraph_Free ((void **) &X, NULL) ;
// printf ("independent set found: %.16g of %.16g nodes\n",
// (double) isize, (double) n) ;
//--------------------------------------------------------------------------
// verify the result
//--------------------------------------------------------------------------
// C = A(I,I) must be empty, except for diagonal entries
GRB_TRY (GrB_Matrix_new (&C, GrB_BOOL, isize, isize)) ;
GRB_TRY (GrB_Matrix_extract (C, NULL, NULL, A, I, isize, I, isize, NULL)) ;
GRB_TRY (GrB_select (C, NULL, NULL, GrB_OFFDIAG, C, 0, NULL)) ;
GRB_TRY (GrB_Matrix_nvals (&nvals, C)) ;
LG_ASSERT_MSG (nvals == 0, -1, "error! A(I,I) has an edge!\n") ;
GrB_Matrix_free (&C) ;
// now check if all other nodes are adjacent to the iset
// e = iset
GrB_Vector e = NULL ;
GRB_TRY (GrB_Vector_dup (&e, iset)) ;
// e = e || ignore_node
int64_t ignored = 0 ;
if (ignore_node != NULL)
{
GRB_TRY (GrB_eWiseAdd (e, NULL, NULL, GrB_LOR, e, ignore_node, NULL)) ;
GRB_TRY (GrB_reduce (&ignored, NULL, GrB_PLUS_MONOID_INT64,
ignore_node, NULL)) ;
}
// e = (e || A*iset), using the structural semiring
GRB_TRY (GrB_vxm (e, NULL, GrB_LOR, LAGraph_any_one_bool, iset, A, NULL)) ;
// drop explicit zeros from e
// e<e.replace> = e
GRB_TRY (GrB_assign (e, e, NULL, e, GrB_ALL, n, GrB_DESC_R)) ;
GRB_TRY (GrB_Vector_nvals (&nvals, e)) ;
GrB_Vector_free (&e) ;
LG_ASSERT_MSG (nvals == n, -1, "error! A (I,I is not maximal!\n") ;
LAGraph_Free ((void **) &I, NULL) ;
printf ("maximal independent set OK %.16g of %.16g nodes",
(double) isize, (double) n) ;
if (ignored > 0) printf (" (%g nodes ignored)\n", (double) ignored) ;
printf ("\n") ;
return (GrB_SUCCESS) ;
}
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